[R-sig-Geo] zip code map - huge files!

[hadley wickham]

Hi Enrico,

I have some code to do map generalisation (reducing map resolution
without visible loss in detail) at
http://github.com/hadley/data-counties/tree/master.  It's applied to
counties data, but would be trivial (if slow) to modify to work with
zip codes instead

Hadley

On Sun, Apr 26, 2009 at 3:06 PM, Enrico Rossi <enrico.a.rossi at gmail.com> wrote:
> Hello,
>
> I have some data at the zip code level, and I'm using the shapefiles
> downloaded from the Census TigerLine website
> (http://www2.census.gov/geo/tiger/TIGER2008/tl_2008_us_zcta5.zip) to
> plot a shaded map of the US. However, the files generated in this way
> are enormous, and take a long time to process, even on a fast machine
> with lots of memory. I'm wondering if there's a more efficient way to
> do this. Maybe rasterize before plotting somehow?
>
> If anyone on this list has experience working with zip-level data, I'd
> appreciate any advice.
>
> Here's some example code like what I'm doing:
>
> # This works, and produces a 1.2GB PDF file! After it's done, I can
> rasterize it using gs to reduce file size, but it takes almost an hour
> library(maptools)
> zip<-readShapePoly("tl_2008_us_zcta5")  # This takes a while!
> val<-runif(length(zip[[1]])) # there are about 32000 zip codes
> pdf("zipplot.pdf")
> plot(zip,xlim=c(-130,-65),ylim=c(20,50),col=grey(val),lty=0)
> dev.off()
> system("gs -dSAFER -dBATCH -dNOPAUSE -sDEVICE=png16m -r300
> -dTextAlphaBits=4 -dGraphicsAlphaBits=4 -dMaxStripSize=8192
> -sOutputFile=zipplot.png zipplot.pdf")
>
> # I've tried plotting directly to png, but it just seems to hang, my
> patience ran out after two hours
> png("zipplot.png")
> plot(zip,xlim=c(-130,-65),ylim=c(20,50),col=grey(val),lty=0)
> dev.off()
>
> # This also takes too long, I never got any output out of it
> library(lattice)
> zip$val<-val
> pdf("zipplot2.pdf")
> spplot(zip,"val",xlim=c(-130,-65),ylim=c(20,50),lty=0)
> dev.off()
>
> Many thanks!
> Enrico Rossi
>
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